To investigate whether O6-methylguanine-DNA methyltransferase (MGMT) interference combined with temozolomide (TMZ) could enhance the therapeutic effect of temozolomide on human drug-resistant melanoma cells A375/TMZ.

A375/TMZ cells were randomly divided into 4 groups, control group (normal culture), MGMTsiRNA group (200 nmol·L^-1 MGMTsiRNA), experimental group (1 600 μmol·L^-1 TMZ) and combined group (transfection of MGMTsiRNA followed by addition of 1 600 μmol·L^-1 TMZ). After 24 h of culture, the proliferation of cells in each group was analyzed by cell counting kit-8 method. Western blotting was used to detect the expression levels of poly ADP-ribose polymerase (PARP), cleaved PARP(cleaved-PARP), DNA-dependent protein kinase catalytic subunit(DNA-PKcs) and nuclear factor kappa-B(NF-κB) proteins in the cells. The expression and distribution of NF-κB proteins in the cells were detected by immunofluorescence.

Cell inhibition rates of control, MGMTsiRNA, experimental and combined groups were 0, (3.45±1.53)%, (51.24±2.73)% and (70.69±4.48)%; the relative expression levels of PARP protein were 0.45±0.08, 0.47±0.06, 0.33±0.04, 0.14±0.03; the relative expression levels of the cleaved-PARP protein were 0.01±0.02、0.01±0.01、0.18±0.03 and 0.36±0.04; the relative expression levels of DNA-PKcs protein were 0.09±0.03, 0.07±0.02, 0.32±0.02 and 0.39±0.04; the relative expression levels of NF-κB protein were 0.35±0.04, 0.36±0.05, 0.20±0.02 and 0.15±0.02. Compared with experimental group or control group, the differences of above indexes were all statistically significant (all P<0.05). Immunofluorescence analysis showed that the average fluorescence intensity of NF-κB in control group, MGMTsiRNA group, experimental group and combined group were (5.26±1.05)%, (7.58±1.18)%, (10.56±1.99)% and (15.47±2.61)%; and compared with the cells in control group and MGMTsiRNA group, combined group showed NF-κB was significantly increased in the nucleus of tumor cells, and the difference was statistically significant (all P<0.01).

MGMTsiRNA combined with TMZ further promotes proliferation inhibition and apoptosis of drug-resistant melanoma A375/TMZ cells by TMZ.